Method for controlling the thickness of a continuous elongated element made of elastomeric material in a process for building tyres

Abstract

A method for controlling the thickness of a continuous elongated element made of elastomeric material, applied according to coils wound on a forming support, includes: advancing a head end of the continuous elongated element toward the forming support; subjecting, during the advancement, the continuous elongated element to a first stretching with a first stretch coefficient before applying on the forming support; and subjecting, during the advancement, the continuous elongated element to a second stretching with a second stretch coefficient during the application on the forming support. During the first stretching, a span of the continuous elongated element adjacent to the head end is stretched with a supplementary stretch coefficient greater than the first stretch coefficient, in a manner so as to confer, also to the span adjacent to the head end, a stretch and a section similar or substantially equivalent to those of the rest of the continuous elongated element.

The invention claimed is: 
     
       1. A process for building a tyre for vehicle wheels, comprising: forming a component made of elastomeric material on a forming support,
 wherein the component made of elastomeric material is obtained by: 
 producing, through an extruder, a continuous elongated element made of elastomeric material; 
 arranging an output opening of the extruder between mutually converging input portions of two opposite conveyor belts; 
 introducing the continuous elongated element between said conveyor belts so that the continuous elongated element is in contact therewith; 
 advancing said continuous elongated element by means of the conveyor belts up to the forming support; 
 applying the continuous elongated element according to coils wound on the forming support, to form the component made of elastomeric material; and 
 wherein a first conveyor belt of the two conveyor belts is mounted on a frame which is moved by an actuator used to vary a mutual compression force between the two conveyor belts during the step of advancing said continuous elongated element, the step of introducing the continuous elongated element causing a head end of the continuous elongated element to move the frame away from a second conveyor belt of the two conveyor belts due to the presence of a thickness of the head end of the continuous elongated element between the two conveyor belts, this movement of the frame away from the second conveyor belt being sensed by a sensor and generating a signal for starting rotation of the forming support on the basis of the signal, when the continuous elongated element is about to reach a terminal end of one of the conveyor belts. 
 
     
     
       2. The process according to  claim 1 , comprising: arranging the output opening at a first distance less than 10 mm from a first contact area between the two opposite conveyor belts and the continuous elongated element. 
     
     
       3. The process according to  claim 2 , wherein said first distance is between 1 mm and 5 mm. 
     
     
       4. The process according to  claim 2 , comprising: providing the terminal end of one of the conveyor belts at a distance less than 100 mm from a first contact area between the continuous elongated element and the forming support. 
     
     
       5. The process according to  claim 4 , wherein the distance from the first contact area between the continuous elongated element and the forming support to the terminal end of one of the conveyor belts is between 10 mm and 50 mm. 
     
     
       6. The process according to  claim 1 , wherein a linear speed of the two conveyor belts is greater than an exit speed of the continuous elongated element from the output opening. 
     
     
       7. The process according to  claim 6 , wherein a ratio between the linear speed and the exit speed is between 1 and 1.5. 
     
     
       8. The process according to  claim 1 , wherein a peripheral speed of the forming support is greater than a linear speed of the two conveyor belts. 
     
     
       9. The process according to  claim 8 , wherein a ratio between the peripheral speed and the linear speed is between 1 and 3. 
     
     
       10. The process according to  claim 6 , wherein the linear speed during an initial transient is greater than an operating linear speed. 
     
     
       11. The process according to  claim 10 , wherein a ratio between the linear speed in the initial transient and the operating linear speed is between about 1 and about 2. 
     
     
       12. The process according to  claim 10 , wherein the linear speed during the initial transient is equal to a peripheral speed of the forming support. 
     
     
       13. The process according to  claim 10 , wherein the linear speed during the initial transient is less than a peripheral speed of the forming support. 
     
     
       14. The process according to  claim 1 , wherein the signal is a function of a vertical movement of an upper belt of said two conveyor belts due to introduction of the continuous elongated element between said conveyor belts. 
     
     
       15. The process according to  claim 1 , comprising: adjusting a vertical force exerted by an upper belt of said two conveyor belts on the continuous elongated element and on a lower belt of said two conveyor belts. 
     
     
       16. The process according to  claim 1 , comprising: stopping the extruder and moving the two conveyor belts for purging the continuous elongated element.